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    <p>When you use <code>[InverseProperty]</code> at both ends of a 1:1 association it is not clear who the principal should be. The principle is the entity the other end (the dependent) refers to by a foreign key. Even though you tell EF that <code>EditoredBy</code> and <code>CurrentlyWorkingBookId</code> both are part of one association it still would be possible to have a foreign key field for <code>EditoredBy</code> in <code>Book</code> (that wouldn't show in the class model).</p> <p>Admittedly, one could contend that you've told EF enough to create the database model properly. EF could have logic that says: if I've been told about one foreign key in a 1:1 association, then I know who the principle should be. However, unfortunately it doesn't.</p> <p>So I would use the fluent API to model this:</p> <pre><code>public class Author { public int AuthorId { get; set; } public ICollection&lt;Book&gt; Books { get; set; } public Book CurrentlyWorkingBook { get; set; } } public class Book { public int BookId { get; set; } public int AuthorId { get; set; } public Author Author { get; set; } public Author EditoredBy { get; set; } } </code></pre> <p>In <code>OnModelCreating</code>:</p> <pre><code>modelBuilder.Entity&lt;Author&gt;() .HasMany(a =&gt; a.Books) .WithRequired(b =&gt; b.Author) .HasForeignKey(b =&gt; b.AuthorId); modelBuilder.Entity&lt;Author&gt;() .HasOptional(a =&gt; a.CurrentlyWorkingBook) .WithOptionalDependent(b =&gt; b.EditoredBy) .Map(m =&gt; m.MapKey("CurrentlyWorkingBookId")); </code></pre> <p>Personally, I like the fluent API because the lambda expressions allow compile-time checks and it is much more conspicuous which ends comprise one association.</p> <p>As you see, <code>CurrentlyWorkingBookId</code> can not be part of the class model in this scenario. That is because an <code>OptionalNavigationPropertyConfiguration</code> (the return type of <code>WithOptionalDependent</code>) doesn't have <code>HasForeignKey</code> method. I'm not sure why not. I think it should be possible to set a primitive FK value (<code>CurrentlyWorkingBookId</code>) as well as a reference property (<code>CurrentlyWorkingBook</code>).</p>
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    1. COThanks for the explanation, it's exactly what I needed :)
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